The manufacture of wood products such as fiberboard and Oriented Strands Board (OSB) from a mixture of wood fibers or chips, wax emulsion and adhesives is well known. Typically, the wood fibers or chips are mixed with a suitable adhesive and wax emulsion and the mixture is then matted and pressed under high pressure and temperature to form a rigid, dense panel. OSB is manufactured using strands sliced from logs in the orientation of the grain. Typically the strands are 4-6 inches in length and 1 inch wide and have a uniform thickness. After drying and sorting, the strands are mixed with the wax and adhesive and oriented in layers. The strands in the layers which will form the exterior surface of the panel are aligned in the long direction of the panel while the inner layers are cross-aligned to the surface layers.
The adhesives commonly employed in the manufacture of OSB include phenolic resins or isocyanate binders. Phenolic resins, produced by reacting phenol with formaldehyde under alkaline conditions have been used for many years. Recently, there have been concerns raised about the production, use and handling of such resins and a number of manufacturers have switched to using isocyanate binders. Liquid polymeric dimethyl phenate di-isocyanate (pMDI) is now becoming the binder of choice. pMDI is an excellent adhesive and provide advantages for the board over other adhesives. However, pMDI provides adhesions not only for the wood fibers, also for the boards to the metal press platens, caul plates or stainless steel screens used in the manufacturing process. Therefore, many OSB producers will use a surface layer of non-pMDI bonded wood chips, such as Phenol formaldehyde resin, and use pMDI in the core layer of the board to prevent the adhesion between pMDI in the OSB and the metal surfaces. This complicated surface-core sandwiching process has increased the cost of board manufacturing, and has prevented the industry from benefiting fully from pMDI adhesive.
There have been attempts to overcome the above bonding to the metal surfaces through the use of release agents. Conventional release agents as used in the industry do not provide satisfactory release. Some of these require elaborate and costly processes for pre-treatment of the press platens, such as applying internal and external release agents, multiple coatings and baking the platens. Other release agents can provide good release, but must be applied in high concentration of up to 80% and require much lower press temperatures and longer press time, thus increasing production time and cost. Some release agents based on higher surface active materials such as silicones may remain associated with the finished OSB surface and thus affect the paintability of the OSB. Up to today, a satisfactory release agent for fully pMDI bonded OS is still not available. Thus there still remains a need for a pMDI release agent which will provide the release between the board and the metal surfaces using a simple application process and allow for production of OSB at high temperature, such as 410° F., without causing excessive press buildup.